1. Field
The invention is in the field of treating and conveying apparatus, such as food freezing, cooling, heating, or cooking apparatus.
2. State of the Art
Various types of fluidized bed conveying apparatus are known as are various types of food cooling, freezing, heating, and cooking apparatus wherein food products are cooled or heated while being conveyed through the apparatus. An example of a combination of such apparatus is a fluidized bed dryer which utilizes a hot air stream passing upwards through a directional oscillating or vibrating perforated plate onto which is fed a stream of particles to be dried, the air stream lifting and passing around and between the particles causing a transfer of heat from the air stream to the particles and a transfer of moisture from the particles to the air stream.
Freezing apparatus is also known wherein a continuous upward spiraling mechanical conveyor conveys various random shaped products in a spiral path through a housing containing refrigerated air. The products freeze while being conveyed. Typically, a freezer of this type is very space and heat transfer inefficient and expensive to build.
U.S. Pat. No. 4,177,647 shows a freezer having a helical conveyance deck down which relatively large packages of packaged product flow by gravity on a thin layer of pressurized freezing air. Rectangular apertures open from a plenum chamber through the conveyance deck to provide an angled flow of pressurized freezing air. Blowers are positioned horizontally or at an angle to the axis of the helical conveyance deck to draw air over refrigeration coils and supply freezing pressurized air to the plenum chamber.
According to the invention, a treating apparatus particularly useful for treating food items such as by freezing, cooling, drying, warming, or cooking such items, includes an inclined track or trough having perforations through which air or other treating gas flows to lift and support such items as they move by gravity down the trough. The trough preferably has a symetrical spiral or helical configuration. The apparatus works well as a freezing device with refrigerated air used to support and treat (cool and freeze) the items as they flow down the trough. The apparatus can also be used to cook items by using hot air of appropriate temperature rather than refrigerated air. The apparatus can also be used for cooling using ambient or cooled air, for drying using dry air, for smoking or flavoring using smoke or flavored air, or for various other uses.
A preferred embodiment of the invention, when used as a continuous freezer, consists of a spiraling trough into which items to be frozen are fed in at the top, with the items then spiraling downwards by gravity in the trough in a substantially circular or elliptical path. A pressurized gas or air stream is forced into a continuous cavity or plenum chamber under the spiraling perforated plate bottom of the continuous spiraling trough, floating the items above the perforated plate. The spiraling trough follows a continuous downward path which the individual pieces or items of product being treated follow; being conveyed by gravity and supported by floating on the pressurized air or gas stream in a near frictionless travel, until the items reach the bottom of the spiral and pass out of the spiral by a straight outlet extension of the spiral conveying means. With treatment completed, the items pass from the outlet to other conveying or collecting means to move the items to further processing, packaging, or storage.
The spiral conveying apparatus forms a symmetrical housing or xe2x80x9cspiral drumxe2x80x9d enclosure in which a fan is placed to provide circulating gas and to provide pressure in the plenum chamber under the spiraling perforated plate. This fan is preferably a centrifugal or plug fan on a vertical shaft extending up and into the center of the spiral drum. The gas enters a duct leading into the center of the centrifugal fan rotor where it is forced through the fan into the open area forming a pressure chamber inside the spiral drum, then into the plenum chamber and through the perforated plate in the product trough, and around the product being conveyed and treated. When the apparatus of the invention is being used as a freezer, the gas may be conventional refrigerated air, or the gas may be cooled by injecting liquid cryogenic gas such as liquified nitrogen or carbon dioxide into the refrigerated air or into ambient or otherwise cooled air. When used as a baking, cooling, or drying device, it may be operated with hot air, ambient air, or dry air. The apparatus may contain a heat or refrigeration source or heated, refrigerated, or cryogenic gas may be fed to the apparatus or the apparatus may be located in a refrigerated or heated compartment, space, or room. The gas may be recirculated or merely exhausted. The fan which supplies the pressurized air stream to the spiral is located inside the spiral drum. The duct leading to the center of the fan may conveniently be a gas inlet extending from the top of the housing or spiral drum to the inside of the fan.